The present invention relates to an improved magnetic sensing proximity detector. Magnetic sensing proximity detectors have been used previously to detect the close presence of a ferrous metal mass. In one form these detectors have includes a central hollow magnet with end magnets supported on a rod connecting them which extends through the opening in the central magnet. A switch is connected at one end of the two connected magnets to be operated by the movement of such two magnets relative to the central magnet and the housing in which it is secured. The approach of a ferrous metal close to the end of the magnet away from the switch end causes the magnets and their connecting rod to move toward the ferrous metal to thus change the position of the switch. An example of this type of magnetic sensing proximity switch is disclosed in U.S. Pat. No. 4,117,431.
Another type of magnetic sensing proximity detector is shown in U.S. Pat. No. 4,674,338 in which a central magnet is positioned within two annular magnets so that the movement of the central magnet which is normally biased in one direction by the positioning of the poles of the three magnets, moves in the opposite direction when a magnetic material approaches sufficiently close to change the forces on the central magnet to overcome the force biasing it toward the one direction.
A further type of magnetic sensing proximity detector is shown in U.S. Pat. Nos. 3,176,096 and 4,225,837 wherein side-by-side magnets are used so that the position of the switch arm is normally in one position and pivots to the opposite position on the approach of a ferrous metal within the range of sensitivity of the detector. The latter patent is stated to be an improvement on the former patent.
One disadvantage which has been experienced with the prior magnetic sensing proximity detectors is their very limited range in which they can sense the approach a ferrous metal material and the fact that such prior devices are not adjustable to preselect the exact point at which the approach of ferrous metal causes the detector to change its position.